The present invention relates improved firing angle control circuits of the thyristors in a voltage control circuit containing reverse parallel connections of a thyristor and a diode or reverse parallel connections of thyristors in at least two phases of the three-phase AC circuit.
The prior art three-phase AC voltage control circuit will be illustrated.
FIG. 1 is a prior art circuit diagram and
FIG. 2 shows voltage waveforms in various parts in the circuit.